Sealing paint

For a Christmas gift for my Mom I'm making her a life-sized set of characters from the Grinch Who Stole Christmas. They're cut out of half inch plywood and painted to look like the characters. I have the Grinch, Max the dog, and Cindy lou-who done. I need to do a few more who's and a tree. But with the fact they're going outside, I think the paint needs to be sealed to protect it against the weather.